Current immunoassays and biomolecule binding assays typically require multiple steps and sophisticated equipment to perform the assays. The lack of sensitivity and the complexity involved in performing such heterogeneous assays arises from the specific need to separate labeled from unlabeled specific binding partners.
Attempts to develop assays based on the local surface plasmon resonance (LSPR) properties of noble metal nanoparticles have been made (Tokel et al., Chem Rev., Vol. 114: 5728-5752, 2014). LSPR is the collective oscillation of electrons in nanometer-sized structures induced by incident light. Metallic nanoparticles have a strong electromagnetic response to refractive index changes in their immediate vicinity and thus shifts in the resonance frequency of the nanoparticles can be measured as an indicator of molecules binding to the nanoparticle surface. Although metallic nanoparticles, particularly gold nanoparticles, have been employed in diagnostic assays to detect binding events, such assays generally suffer from low sensitivity and cannot be used to quantitatively monitor the kinetics of sequential binding events.
Thus, improved assay methods employing a homogenous format while providing increased sensitivity are needed. Assays utilizing standard laboratory techniques, such as spectroscopy, would also be desirable.